These are the free dice which appeared in this video on Matt's Stand-up Maths youtube channel:
They are free as long as you pay the postage to get them to you. Only one each please! If you try to order more than one: only one will be sent to you anyway.
If they run out: I'll post out the normal d12 and d20s from the video as well. But once they are gone: they're all gone!